1. Field of the Invention
The present invention relates to an electrical hand-held power tool with an electric motor having a stator housing and a device for reversing the rotational direction of the electric motor. The reversing device has a contact carrier fixedly securable on the stator housing with releasable connection means. On the contact carrier, there are provided field contact means for an electrical connection with the stator winding and fixed contacts means electrically connected with the field contact means. The reversing device further has a brush carrier rotatable relative to the contact carrier and on which there are provided two carbon guides and switching contact means electrically connected with carbon guides. The switching contact means are electrically connectable with fixed contacts of the contact carrier in respective rotational end positions.
2. Description of the Prior Art
Electrical hand-held tools of the type discussed above have a universal motor with a commutator that is electrically connected with carbon brushes arranged in carbon guides. In order to achieve an optional commutation for both rotational directions, both carbon guides are rotated in a circumferential direction, together with the carbon guide-supporting, brush carrier, upon changing from clockwise rotation to counterclockwise rotation, with a handle accessible from outside. With the rotation of the brush carrier, simultaneously reversal of the carbon brushes relative to the fixed contact means takes place and, thus, a change in the rotational direction of the motor.
German Publication DE 195 45 651A1 discloses an electrical hand-held power tool with a reversible electric motor. There is further provided a device for reversing the carbon brushes and which has a contact plate and a brush carrier. The contact plate is fixedly secured on the stator of the electric motor by plug connection. From the contact plate, hook elements project which engage the brush carrier from behind and, thus, rotatably supporting the same on the contact plate. In the contact plate, there is provided a groove in which, in an assembled condition, a switchable contact system for reversing the carbon brushes is located. At the free end, a shoulder-forming edge of the brush carrier abuts the contact plate for sealing purposes.
In this way, on one hand, penetration of dust into the contact system is prevented and, on the other hand, axial position of the brush carrier is secured. Moreover, the motor, the contact plate, and the brush carrier can be separately produced and easily assembled, which reduces the costs of manufacturing of the electrical hand-held power tool.
The drawback of the known reversing device consists in that between the brush carrier and the contact plate a certain clearance must be maintained in order to ensure the rotation of the brush carrier. In addition, the position of the contact plate relative to the stator, in particular, in case the contact plate is attached to the stator by using plug connection means, also requires some clearance and varies dependent on manufacturing tolerances. Therefore, the fitting position of the carbon brushes relative to the commutator depends to a significant extent on tolerances, which results in poor commutation and can lead to an increased wear of the carbon brushes.
Accordingly, an object of the present invention is an electrical hand-held power tool in which the foregoing drawbacks of the prior art tool are eliminated.
Another object of the present invention is to provide an electrical hand-held power tool in which a precise fitting position of the carbon brushes relative to the commutator is ensured.
A further object of the present invention is to provide an electrical hand-held power tool that can be cost-effectively produced.